The invention relates to an electric incandescent lamp provided with
a tubular glass lamp vessel which is sealed in a gas-tight manner and has a seal at a first end;
current supply conductors entering the lamp vessel through said seal;
a helically wound filament which is longitudinally arranged in the lamp vessel and has at each of its ends a limb which is connected to a respective current supply conductor;
an elongated concave reflecting screen in the lamp vessel, which extends along the filament whilst facing said filament with its concave side, this screen being curved substantially spherically at its end facing the said seal, has a vane at its other end extending longitudinally in the lamp vessel and has a flat base portion.
Such a lamp is known inter alia from European Patent Application No. 0098905 (Cibie Projecteurs 25 01 84). The lamp can be used as a headlight in vehicles, the filament then producing a dipped beam. If a second filament not cooperating with the concave screen is arranged in the lamp vessel, a main beam can be obtained thereby. Such a lamp having two longitudinal filaments and a halogen-containing gas filling is designated as an H4 lamp.
Many vehicles have headlights which are provided with a flattened paraboloidal reflector. With the use of an incandescent lamp of the kind described in the opening paragraph in a flattened reflector, the reflecting screen reflects a considerable quantity of light onto a flat portion of the reflector. This light provides a very small contribution to the dipped beam emitted by the headlight.
According to the invention described in the Application No. 0098905, a reflecting screen is used which is curved spherically at its end remote from the seal. As a result, a larger quantity of the light generated by the filament is contained in the beam emitted by the headlight. However, a disadvantage of this screen is that it does not exhibit a longitudinal vane. A further disadvantage is that a differently shaped screen has to be used.